The development of differences between male and female nervous systems is essential for sexual behavior and reproduction. However, little is understood about the mechanisms by which sex-determining genes interact with neuronal genes to specify sexual dimorphism. Development of C. elegans male-specific neurons depends on a conserved sexual regulator, the DM domain protein MAB-3, and a conserved neural regulator, the bHLH protein LIN-32. C. elegans provides a genetically tractable system for identifying novel genes that act with MAB-3 and LIN- 32 to specify V rays, male-specific sensory structures required for mating. To investigate how MAB-3 and LIN-32 interact to specify V rays, mutations identified in a screen for suppressors of the mab-3 V ray defect (smt mutations) will be mapped, cloned, and molecularly characterized. The requirement for smt genes during V ray development will be determined by analysis of sensory ray patterning and neurotransmitter expression in smt mutant males. Genetic and molecular interactions of smt genes with known regulators of V ray differentiation will determine whether smt genes act in the mab-3 or lin-32 genetic pathway, smt expression will be analyzed to identify the developmental stages and cells in which smt genes act. The smt genes interact genetically with mab-3 and lin-32, which play a conserved role in vertebrate sexual and nervous system development, respectively. As mab-3 and lin-32-interacting loci, the smt genes may define a new class of conserved regulators of sex-specific nervous system development.